Cylinders of internal combustion engines must be sealed airtight when the valves are closed to ensure efficient fuel consumption and transfer of power. Cylinders having perfectly matched valve heads and valve seats produce an optimal seal. Since contact surfaces of the valves and valve seats are subject to wear and other degrading factors that effect the contact surface textures, these surfaces must be modified to re-establish the high quality seal.
It is well known among vehicle mechanics that valve seats can be machined to remove the outer surface of the seat to expose a smooth and uniform contact surface by a technique commonly referred to as xe2x80x9clappingxe2x80x9d. This lapping technique is accomplished by removing the cylinder head from the engine and machining the valve seats with a cutting blade. Typically, a valve seat has a profile with three different angles: a throat angle, a valve seat angle, and a top angle. Thus, a xe2x80x9cthree-anglexe2x80x9d cutting blade or bit is used to machine a valve seat wherein each angle of the three-angle cutting blade corresponds to one of the valve seat angles to be machined. Three-angle cutting blades vary in size and shape depending on the type of cylinder head valve seat being machined. These three-angle cutting blades are currently used by valve seat and guide manufacturers.
A disadvantage of the lapping technique is the risk of damage to the surface finish from vibrations, chattering, or undulations generated from flexion of the cutting bits. This problem develops because certain large-diameter cylinder head valve seat shapes require a three-angle cutting blade with a long cutting edge/surface. Cutting efforts with this long cutting edge/surface create flexions at the level of the spindle of the cutting machine or on the cylinder head, especially when dealing with valve seat material that is difficult to machine. These flexions generate vibrations, chattering, or undulations which, in turn, damage the surface finish of the valve seat resulting in a machined valve seat that is not acceptable by Original Equipment Manufacturer (OEM) standards.
Another disadvantage of the lapping technique is a de-centering phenomena. As stated above, cutting efforts with a long cutting edge/surface create flexions. These flexions create an unbalanced radial cutting effort which de-centers the three-angle cutting blade.
Still another disadvantage of the lapping technique is the large number of three-angle cutting blades needed to machine different types of valve seats. Each type of engine has a different valve seat profile. Thus, one or more unique three-angle cutting blades may be needed for each type of engine.
In view of the aforementioned inadequacies of the prior art, the need exists for a cutting tool and a method to machine valve seats that substantially reduces flexions during machining and uses a universal cutting blade.
It is an advantage of the present invention to provide one universal cutting bit and bit holder having the ability to precisely machine an unlimited number of valve seat shapes concave, convex, and vertical bores.
It is also an advantage of the present invention to substantially reduce flexion of the cutting bit during valve seat machining.
It is another advantage of the present invention to eliminate de-centering phenomena due to unbalanced radial efforts from flexion.
Yet another advantage of the present invention is to eliminate vibrations, chattering, and undulations to provide improved roundness in a valve seat.
Still another advantage of the present invention is to provide concentric machining for multiple contours within a single valve seat.
In an exemplary embodiment, the present invention is a machining head of a machining apparatus comprising a spindle, a carriage head, a carriage head holder, a pinion feed driving assembly, and a universal cutting blade. A fixed pilot is attached to the bottom of the carriage head along the z-axis of a machine spindle to provide a means for centering the machining head in a valve guide of a cylinder head. The carriage head holder attaches to an extension of the machine spindle so that when the machine spindle is rotated, the machining head rotates. The carriage head is attached to the carriage head holder at an inclined angle relative to the bottom surface of the carriage head. The pinion feed driving assembly provides control of the inward and outward movement of the carriage head. The universal cutting blade is mounted on the carriage head through one of a plurality of mounting holes. The machining head can be utilized with virtually any conventional valve seat machining system, but is preferably used with the systems disclosed in U.S. Pat. No. 5,613,809, 5725,335, and 5,829,928 of Harmand, et al. (hereinafter the ""809, ""335, and ""928 patent, respectively) which are incorporated herein by reference.
The machining apparatus of the preferred embodiment comprises a driving system, a machining head as described above, a pilot, a depth gauge, and a system controller. The driving system further comprises a machining sphere, a machine spindle, a spindle sheath, a drive motor, and a stepper motor. The spindle sheath is disposed within and supported by the machine sphere. The spindle sheath is fixed within the x- and y-axis, but can move along the z-axis by the stepper motor. The stepper motor is electrically connected and controlled by the system controller. The machine spindle is disposed within the spindle sheath and rotates around its z-axis through a drive motor. The drive motor rotating the machine spindle is electrically connected to and controlled by the system controller. The depth gauge is disposed on the spindle sheath by a fixed arm and is electrically connected to the system controller. The depth gauge measures the distance between a top surface of a cylinder head and the cutting blade.
The system controller includes a memory which contains software for controlling the operation of the cutting tool. This system controller includes a user interface at which an operator can input the parameters that define the geometry of a valve seat profile. These parameters are used by the system controller to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, the inward/outward displacement of the carriage head, and the number of rotations needed to machine a segment of the valve seat profile. The system controller uses a look-up table, stored externally or within internal memory, and the input information is used to determine the vertical feed rate of the machine spindle, the length of the vertical displacement of the spindle to machine the segment, and the number of rotations needed to machine a segment of the valve seat profile. The operator simply needs to center the spindle, activate the system after the initial input of information for a given cylinder head and valve seat profile, and re-center on each subsequent valve seat before activation.